BFE measures how well a mask filters bacteria-sized particles, PFE measures how well it filters sub-micron particles, and Delta P measures how much breathing effort the mask creates. All three are performance measurements taken on the mask material, and the three are read together because they pull against each other: a mask can filter more by being denser, and denser material is harder to breathe through. The test methods sit inside ASTM F2100, the specification that Canadian and United States buyers most often reference when they specify a medical face mask. Here is what each measurement actually does.
What Does BFE Measure?
BFE stands for bacterial filtration efficiency. It is a measure of how well the mask material stops bacteria-carrying aerosol droplets from passing through it, expressed as a percentage of the challenge aerosol that the material captures.
The test drives a bacterial aerosol at the material sample at a defined flow rate, counts what gets through, and compares that with what was presented. The particle sizes in the challenge aerosol cluster around the size of droplets that carry bacteria, which is why BFE is described as a bacterial filtration measurement rather than a general particle measurement. A higher BFE means the material captures a larger share of that challenge.
One thing BFE is not: it is not a wear test, and it is not a fit test. It measures material performance on a bench, not leakage around the edges of a mask on a face.
What Does PFE Measure?
PFE stands for particle filtration efficiency, measured with a challenge aerosol of sub-micron particles — smaller than the droplets used in the BFE method. Because the particles are smaller, PFE is the harder of the two efficiency numbers for a material to achieve, and it is the measurement that separates a simple three-ply mask from a mask built to a higher barrier specification.
The relationship between the two numbers is worth keeping clear in your head. BFE and PFE are both percentages, both higher-is-better, and they are measured with different aerosols, so a mask can score well on one and less well on the other. When a specification lists both, read them as a pair rather than treating one as a substitute for the other. The explanation of the ASTM F2100 levels for medical face masks shows how the levels are set from these measurements together.
What Is Delta P Measuring?
Delta P, written ΔP, is differential pressure, and it is the odd one out in the trio because lower is better. Delta P is the pressure drop across the mask material at a stated airflow, which is a proxy for how much resistance the mask puts up to the wearer's breathing.
A high Delta P means a material that filters more but breathes harder. A low Delta P means a lighter, more breathable material that filters less. This is the trade-off the specification is built around: masks are not simply ranked by filtration, they are qualified on filtration and on breathability together, and the Delta P ceiling is what stops a manufacturer from meeting the filtration requirement with a material nobody can tolerate for a shift.
Delta P is measured on material, so it does not capture the effect of a poorly fitting mask, a saturated mask, or a mask worn over another mask. Those are behavioural and fit effects, not material measurements.
| Term | What it stands for | What the test does | Direction that is better |
|---|---|---|---|
| BFE | Bacterial filtration efficiency | Challenges the material with a bacteria-carrying aerosol of droplet size and measures capture | Higher percentage |
| PFE | Particle filtration efficiency | Challenges the material with a sub-micron particle aerosol and measures capture | Higher percentage |
| Delta P | Differential pressure | Measures pressure drop across the material at a stated airflow | Lower value |
Which Measurement Should a Buyer Read First?
None of them in isolation. The useful buying sequence is: confirm the level the task requires, then read the filtration figures as a pair, then read Delta P as the comfort constraint that separates two materials that both meet the filtration threshold.
Two further points keep the numbers honest. First, all three are material measurements, so a mask that tests well can still leak at the cheeks and nose if it does not fit the wearer; fit is a separate issue from filtration. Second, blood and fluid resistance is a different measurement again, taken under its own test method, and it is not implied by a strong PFE. The explanation of the ISO 22609 blood splash resistance test method covers how that requirement is demonstrated separately.
A mask that carries the ASTM level and the associated documentation makes the reading simple: the 3-ply ASTM Level 3 face masks, 50 pack are specified to that framework, and the associated test figures travel with the product documentation.
Where Do These Terms Appear in Practice?
You will meet BFE, PFE and Delta P in three places: on a supplier's specification sheet, inside a test report from a third-party laboratory, and in a procurement requirement written by an infection prevention or occupational health reviewer. In all three, the same discipline applies — ask which test method was used, which sample was tested, and whether the figure quoted is for the material or for a finished product.
Reading a test report as a whole, rather than lifting one number from it, is the difference between knowing what a mask was shown to do and repeating a marketing shorthand.
Related reading
- ASTM F2100 levels explained for medical face masks
- ISO 22609 blood splash resistance: test method and claims
- For clinics collection
Ordering for a clinic, lab or care home? Wholesale and multi-site ordering covers case pricing and account setup, and the B2B wholesale collection lists the lines stocked for institutional buyers.
Frequently Asked Questions
What is the difference between BFE and PFE?
Both are filtration efficiency percentages, but they use different challenge aerosols. BFE uses a bacteria-carrying aerosol of droplet size, while PFE uses smaller sub-micron particles, which generally makes PFE the harder figure to achieve.
Is a lower Delta P always better?
Lower Delta P means easier breathing, which is better for wearer comfort and tolerance, but on its own it says nothing about filtration. Read Delta P together with the filtration figures rather than as a standalone ranking.
Do these tests tell me whether a mask fits?
No. BFE, PFE and Delta P are measurements taken on mask material, so they describe the material rather than the fit. Leakage at the edges of a mask is a separate issue from how the material performs on a bench test.
Does a high PFE mean the mask is fluid resistant?
No. Fluid and blood splash resistance is demonstrated by a separate test method, and it is not implied by a strong particle filtration result. Check the fluid resistance requirement independently.
CliniEco Medical is a licensed medical device establishment (MDEL #35334).
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